Efforts are currently being made for the Third Generation Partnership Project (3GPP) long term evolution (LTE) program to introduce new technology, new architecture and new LTE settings and configurations in order to provide improved spectral efficiency, reduced latency, and improved utilization of radio resources to provide faster user experiences and richer applications and services at a lower cost.
As part of these efforts, the 3GPP LTE program is working on introducing the concept of a home evolved Node-B (HNB) in LTE, (and also, possibly in a parallel fashion, in Release 8 wideband code division multiple access (WCDMA), global system for mobile communications (GSM) enhanced data rates for GSM evolution (EDGE) radio access network (GERAN) and other cellular standards). The HNB is intended to be similar to a wireless local area network (WLAN) access point (AP), and is to be designed in a manner that allows access to cellular services to users over extremely small service areas, (e.g., homes or small offices). This can be particularly useful in areas where cellular networks have not been deployed and/or legacy radio access technology (RAT) coverage exists, as well as in areas where cellular coverage may be faint or non-existent for radio related reasons, (e.g., an underground metro or shopping mall). The subscriber, (e.g., an individual or an organization), may deploy an HNB over an area where such service is desired.
An HNB in an LTE network may be identified by means of a unique tracking area (TA) identity (ID), cell ID, or a combination of both. The problem that may be encountered with this approach is that in order to read the ID of a cell, a wireless transmit/receive unit (WTRU) has to acquire the cell broadcast information of the HNB. However, when the WTRU is in a connected mode while performing measurements, the WTRU does not usually read the radio resource control (RRC) layer broadcast channel. However, if the WTRU were to do so, it might lead to unacceptable performance requirements since there may be many HNBs in the vicinity.
One possible solution is that HNBs be identified at the physical (PHY) layer by means of a reserved physical layer synchronization signal. In LTE, there are three possible primary synchronization channels (P-SCH) and 170 possible secondary synchronization channels (S-SCH), for a total of 510 unique physical layer cell IDs. However, a problem with this solution is that the PHY layer cell ID of two or more HNBs may collide, and the WTRU may not be able to distinguish between them.
In earlier systems, cell planning techniques were sufficient to ensure that there was no collision between neighboring cells of different operators. However, with potentially hundreds of HNBs in the vicinity of the WTRU, (belonging to potentially multiple operators), cell planning techniques may be less effective. In such a scenario, it becomes necessary to address the issue of WTRU procedures when a collision between neighboring cells is detected.